It is known to use a sound barrier wall for reducing and impeding the transmission of sound waves. A sound barrier wall can, for example, be installed alongside an expressway to confine and minimize traffic noise generated by passing automobiles. It is also known to add resonance equipment on top of a sound barrier wall which includes several different type of Helmholtz resonators responsive to selected resonance frequencies of the source of noise to be abated so as to more effectively minimize the noise level at the barrier wall and confine the level of noise to an acceptable level. An arrangement consisting of a combination of a sound barrier wall and resonance equipment is disclosed in Japanese Patent No. P3485552 for reducing noise from e.g. traffic to an acceptable low level. The sound resonance equipment disclosed in this patent publication includes an outer shell which surrounds a plurality of resonant chambers responsive to different resonance frequencies and includes means for mounting the resonance equipment to the top of a vertically installed sound barrier wall to form a substantially uniform arrangement of an equal number of resonant chambers on each opposite side of the sound barrier wall.
Although the sound resonance equipment taught and described in the aforementioned Japanese Patent No. P3485552 is effective for reducing noise the construction and installation requirements to form a substantially uniform arrangement of an equal number of resonant chambers on each opposite side of the sound barrier wall is expensive, difficult to maintain and unsightly in appearance. Less expensive noise reducing equipment which can be more easily installed and maintained without any noticeable decrease in its effectiveness to abate noise is the principal object of the present invention.